$date = "2000-12-1";

unless ($date =~ m/(\d\d\d\d)-(\d\d?)-(\d\d?)/) {
    die "Invalid date format\n";
}

# put captured data from regex into appropriate vars
my ($year,$month,$day) = ($1,$2,$3);
die "Invalid year!" if $year < 1900 or $year > 2100;
die "Invalid month!" if $month < 1 or $month > 12;
die "Invalid day!" if $day <1 or $day > 31;

print "Date OK!";